European Journal of Wildlife Research

, Volume 55, Issue 2, pp 117–123

Selective culling of Iberian red deer stags (Cervus elaphus hispanicus) by selective montería in Spain

Authors

  • Jerónimo Torres-Porras
    • Evolutionary Biology, Ethology and Wildlife Management Research GroupUniversity of Extremadura
    • Evolutionary Biology, Ethology and Wildlife Management Research GroupUniversity of Extremadura
  • Javier Pérez-González
    • Evolutionary Biology, Ethology and Wildlife Management Research GroupUniversity of Extremadura
Original Paper

DOI: 10.1007/s10344-008-0225-4

Cite this article as:
Torres-Porras, J., Carranza, J. & Pérez-González, J. Eur J Wildl Res (2009) 55: 117. doi:10.1007/s10344-008-0225-4

Abstract

Hunting can affect animal populations not only by increasing mortality but also by introducing selection components associated with particular features of individuals. In addition to the most widespread hunting system in Spain for Iberian red deer stags (Cervus elaphus hispanicus) called montería, there are also selective monterías aimed at culling poor-trophy males in order to improve the average quality of the trophies for commercial hunt. This way of removing poor-trophy males contrasts with the most common procedure of shooting individual males by selective stalking that is used in other areas of Europe. Also, due to the hunting procedure by which most deer are shot while running chased by dogs, it is doubtful whether hunters are actually producing a selective impact on deer populations. In this paper, we compare data of males shot in commercial montería and in selective montería in Southern Spain. We found that males in selective montería were smaller in body size and in antler size than in commercial hunts, even correcting by age, although the selective effect was stronger at some ages. We discuss the implications of this practice for sustainable use and conservation.

Keywords

Iberian red deerCervus elaphusHuntingSelective cullingManagementUngulates

Introduction

Modern hunting by humans represents a new cause of mortality in many natural populations. Human-induced mortality may be higher than natural recruitment and lead to population decline (Bubenik 1987; Crichton 1992; Wilton 1992, 1995), but hunting also commonly produces differential effects over some particular age and sex classes (Ginsberg and Milner-Gulland 1994; Langvatn and Loison 1999). For example, hunters tend to prefer trophy individuals so that hunting commonly focuses on males rather than females or calves (Schwartz 1992; Forsyth 1999), which may produce a bias in the sex ratio in favor of females, potentially affecting population dynamics (Ginsberg and Milner-Gulland 1994; Milner-Gulland et al. 2003).

Hunting may introduce an element of artificial selection in natural populations. Although even random mortality when elevated may affect the balance between natural selection and genetic drift (Hartl and Clark 1997), mortality caused by different hunting types may show considerable departures from random with respect to the age or phenotype of individuals. For example, it is known that mortality likely departs from random in the case of trophy hunting. Trophy hunting on some big game species has been demonstrated to introduce a selective pressure favoring individuals with relatively smaller secondary sexual traits, with noticeable genetic effects after a few generations (e.g., Coltman et al. 2003; Garel et al. 2007).

Management of hunting populations to produce trophy individuals, which render economic profits, usually leads to the selective culling of those with relatively smaller trophies. Selective culling is a management practice aimed at increasing size and value of trophies either by increasing the mean size of breeding males with possible genetic effects or simply by removing smaller individuals prior to the hunting season, thus trying to increase the average size of those offered to hunters in commercial hunts (Ginsberg and Milner-Gulland 1994; Langvatn and Loison 1999).

Even if the criteria used by hunters in selective culling may be clear at focusing on those individuals that are of lower development than expected for their age, achieving this objective entails practical problems in the field so that the actual effect of selective culling on population structure is unknown unless a detailed study is made on the age and size of culled individuals with respect to the population or other hunting procedures.

A main difference between our study area and other European red deer populations is that in other populations, selective culling is carried out by stalking, while in our study area, most selective culling is carried out by selective montería (see below). Under this procedure, deer come to hunters’ positions chased by dogs, so hunters presumably have little opportunity to observe and select the individuals to be shot. Thus, actual features of culled animals might depart from culling criteria.

In this study we compare the age, body, and antler size of red deer stags hunted in commercial hunt called montería (commercial montería) with those shot in selective culling (selective montería), with two main purposes: First, to see whether the proposed effect of eliminating those individuals with the poorest trophies is being achieved, and second to infer the possible ecological and evolutionary implications of this practice in the context of hunting exploitation of Iberian red deer (Cervus elaphus hispanicus) populations.

Materials and methods

The study area was located in Southern Iberian Peninsula in the province of Córdoba (Spain). The climate is Mediterranean, with seasonal rains in winter and spring along with dry and hot summers. The dominant vegetation includes tree species such as holm oak (Quercus ilex) and cork oak (Quercus suber), together with reafforestations of stone pine (Pinus pinea) and cluster pine (Pinus pinaster), accompanied of shrub species (Cistus, Phyllirea, Arbutus).

Thousands of red deer stags are hunted every hunting season from October to next February in the Spanish typical commercial hunt called montería. In this type of hunt, packs of dogs are released within a shrub area to move the deer outward to the sites where hunters are placed. Normally, every male deer of 2 years or more can be legally shot. Hunting pressure on males is regulated basically by allowing only one montería per year in the same area. Because hunters can normally shoot every male above 2 years, there is little opportunity for hunting bias to particular males, and montería is the less biased procedure to obtain data from hunted red deer (Martínez et al. 2005). However, there is another type of hunt similar in the organization to a montería, but aimed at eliminating poor-trophy males in order to raise trophy quality in the population as part of the management practices in hunting estates. Under this type of selective culling called “selective montería”, managers tend to remove those males with lower-than-expected antler development (Mesía-Figueroa et al. 1978; Carranza 1999; Carranza and Martínez 2002), which means small antlers for their age, although age estimation may entail difficulties in practice and depends on the conditions to observe the animal before deciding about whether to shoot it.

Data for this study were obtained from animals shot in commercial montería as well as in selective culling of the type selective montería performed in hunting estates as part of their normal game management practices. Our study never provoked hunters to shoot additional deer (see, e.g., Mysterud et al. 2001; Loe et al. 2003; Bonenfant et al. 2003; Carranza et al. 2004 for examples of the use of harvesting data).

Data were collected from 242 deer in eight estates during the hunting seasons 2004–2005 and 2005–2006. For simplicity, we will refer to these seasons as years 2004 and 2005, respectively. Four monterías were selective (N = 89 stags culled), while seven were commercial (N = 153 stags culled). All eight estates regularly performed non-selective and selective monterías, which ensures that our sample for both types of hunt was due to opportunity to collect the data and was not biased by features of the estates.

At the end of each hunting day, we visited the place where culled animals were gathered. For every animal, we recorded a number of measurements in the field and removed mandibles for determining the age in the laboratory.

For body measurements, we used a metric tape of ±0.5 cm accuracy and for the measures of the antlers one of ±0.1 cm. The following measures were taken:
  • Body length (centimeter): measured from the tip of snout to the tip of the tail, excluding the hair and following the dorsal contour of the body of the animal lying on the ground

  • Heart girth (centimeter): chest perimeter behind the foreleg

The following measurements for both sides of the antlers were also taken in the field:
  • Antler length (centimeter): measured from the burr (included) to the longest tip of the antler

  • Burr circumference (centimeter): perimeter of the basal bone protrusion of the antler

  • Number of antler points: total tines ≥2 cm in both antlers

For antler length and burr circumference, we used the mean values from both antlers. It was not possible to take all measurements for all individuals, so sample sizes differ among measurements.

Age was estimated by counting cementum layers at the interradicular pad under the first molar (Mitchell 1967) and checked by eruption patterns in younger animals. Ages are expressed in completed years from birth, so an animal aged N is living its N + 1 year of life, as used for humans.

Data were analyzed by using General Linear Models (GLM; SPSS software vs 11, SPSS, Chicago, IL, USA). To see if age differed between the two types of hunt, we made a GLM with age as the dependent variable, type of hunt (selective or commercial) and year as fixed factors, and estate as a random factor. To investigate whether independent factors influenced morphological variables, we used GLM models with year and type of hunt as fixed factors, estate as random factor, and age and its quadratic term as quantitative covariates. To see the variations of the effect of type of hunt on the dependent variables across the range of ages, we performed new GLM analyses with age as ordinal categorical variable to obtain parameter estimates for the effect of type of hunt at each age. For this last type of analyses, ages from 7 to 11 years were grouped into one category to avoid very small sample size.

Results

Mean age (years) of animals hunted in selective montería was 3.80 ± 1.96 SD compared with 4.52 ± 1.59 SD in commercial montería (GLM: F1,240 = 9.651, p = 0.002). However, the age of culled animals depended mainly on the estate where they were hunted (the effect of type of hunt was not significant when controlled by differences among estates; GLM with age as dependent variable, for factor type of hunt: F1,232 = 1.010, p = 0.316; for factor estates: F1,232 = 3.395, p = 0.002). In our sample of hunted stags, full-grown males were less represented in selective montería: only 17 out of 89 (19.1%) were above 4 years of age in selective montería compared with 68 of 153 (44.4%) in commercial montería.

All measured variables for body size and antler size were smaller in stags culled in selective monterías than in those hunted in commercial monterías (Table 1). This indicated that hunters in selective monterías were in general able to discriminate the size of males to shoot individuals below the average size for their age. Data from the 2-year study did not differ for any of the study variables with the exception of antler length, which was smaller in 2005 than in 2004. Body and antler size differed among estates, but for all variables, the effect of selective hunting was significant after controlling for differences among estates (Table 1). The effect of selective monterías to cull smaller individuals than in commercial monterías was in general consistent with variations in age for most morphological variables (most interactions between type of hunt and age were non-significant), with the exception of heart girth (Table 1).
Table 1

GLM results for the dependent variables of body size and antler size from stags hunted in commercial and selective monterías, with age as a continuous quantitative variable

 

df

F

p

Body length

Intersect

1, 104.22

1,340.00

0.001

Type of hunt

1, 227

5.83

0.017

Year

1, 227

1.15

0.283

Estate

7, 227

9.81

0.001

Age

1, 227

38.47

0.001

Age2

1, 227

22.65

0.001

T. hunt × Age

1, 227

1.18

0.278

Heart girth

Intersect

1, 76.34

1,249.08

0.001

Type of hunt

1, 225

11.72

0.001

Year

1, 225

1.26

0.260

Estate

7, 225

12.96

0.001

Age

1, 225

37.34

0.001

Age2

1, 225

20.74

0.001

T. hunt × Age

1, 225

6.70

0.010

Antler length

Intersect

1, 88.52

31.81

0.001

Type of hunt

1, 204

23.76

0.001

Year

1, 204

5.27

0.023

Estate

7, 204

11.63

0.001

Age

1, 204

69.40

0.001

Age2

1, 204

28.64

0.001

T. hunt × Age

1, 204

2.02

0.156

Burr circumference

Intersect

1, 122.25

101.06

0.001

Type of hunt

1, 206

8.51

0.004

Year

1, 206

0.01

0.909

Estate

6, 206

7.46

0.001

Age

1, 206

44.48

0.001

Age2

1, 206

14.85

0.001

T. hunt × Age

1, 206

0.00

0.972

No. of antler points

Intersect

1, 205.10

7.91

0.005

Type of hunt

1, 219

6.85

0.009

Year

1, 209

0.65

0.410

Estate

7, 219

3.31

0.002

Age

1, 219

74.53

0.001

Age2

1, 219

52.02

0.001

T. hunt × Age

1, 219

0.62

0.429

Factors were type of hunt (commercial or selective) and year, the different estates were introduced as a random factor, age and its quadratic term were introduced as quantitative covariates. The interaction between type of hunt and age was introduced in models to see if the effect of the type of hunt differed with age

Although selectively culled stags were almost always smaller than those culled in commercial monterías, some age classes contributed more than others to these differences (Tables 2 and 3, Figs. 1, 2, 3, 4, 5). For body length, the effect of type of hunt was rather constant across the range of ages (Table 3, Fig. 1), while for hearth girth, the effect of selective hunt was stronger for 2-year-old individuals (Table 3, Fig. 2). Small antlers were strongly selected against by selective culling across the range of ages (Table 2). For antler length and burr circumference, the effect was especially strong for stags just before the reproductive ages (at 4–5 years; Table 3, Figs. 3, 4), while for antler points, the impact of selective culling maintained rather constant across the whole range of ages (Table 3, Fig. 5).
https://static-content.springer.com/image/art%3A10.1007%2Fs10344-008-0225-4/MediaObjects/10344_2008_225_Fig1_HTML.gif
Fig. 1

Comparison of body length for stags hunted in commercial and selective monterías for each age class. Figure shows estimated marginal means ± standard errors from the GLM models of Table 2. Numbers within the figure indicate sample size (number of individuals)

https://static-content.springer.com/image/art%3A10.1007%2Fs10344-008-0225-4/MediaObjects/10344_2008_225_Fig2_HTML.gif
Fig. 2

Comparison of heart girth for stags hunted in commercial and selective monterías for each age class. Figure shows estimated marginal means ± standard errors from the GLM models of Table 2. Numbers within the figure indicate sample size (number of individuals)

https://static-content.springer.com/image/art%3A10.1007%2Fs10344-008-0225-4/MediaObjects/10344_2008_225_Fig3_HTML.gif
Fig. 3

Comparison of antler length for stags hunted in commercial and selective monterías for each age class. Figure shows estimated marginal means ± standard errors from the GLM models of Table 2. Numbers within the figure indicate sample size (number of individuals)

https://static-content.springer.com/image/art%3A10.1007%2Fs10344-008-0225-4/MediaObjects/10344_2008_225_Fig4_HTML.gif
Fig. 4

Comparison of burr circumference for stags hunted in commercial and selective monterías for each age class. Figure shows estimated marginal means ± standard errors from the GLM models of Table 2. Numbers within the figure indicate sample size (number of individuals)

https://static-content.springer.com/image/art%3A10.1007%2Fs10344-008-0225-4/MediaObjects/10344_2008_225_Fig5_HTML.gif
Fig. 5

Comparison of number of antler tines for stags hunted in commercial and selective monterías for each age class. Figure shows estimated marginal means ± standard errors from the GLM models of Table 2. Numbers within the figure indicate sample size (number of individuals)

Table 2

GLM results for the dependent variables of body size and antler size from stags hunted in commercial and selective monterías with age as ordinal categories

 

df

F

p

Body length

Intersect

1, 11

6,765.73

0.001

Type of hunt

1, 220

6.53

0.011

Year

1, 220

0.80

0.371

Estate

7, 220

9.81

0.001

Age

5, 220

14.61

0.001

T. hunt × Age

5, 220

1.18

0.317

Heart girth

Intersect

1, 10,12

5,437.49

0.001

Type of hunt

1, 218

5.94

0.016

Year

1, 218

0.93

0.335

Estate

7, 218

12.24

0.001

Age

5, 218

14.08

0.001

T. hunt × Age

5, 218

1.65

0.146

Antler length

Intersect

1, 10,20

756.92

0.001

Type of hunt

1, 197

30.64

0.001

Year

1, 197

5.13

0.025

Estate

7, 197

11.91

0.001

Age

5, 197

47.55

0.001

T. hunt × Age

5, 197

4.44

0.001

Burr circumference

Intersect

1, 12,33

1,407.06

0.001

Type of hunt

1, 199

15.67

0.001

Year

1, 199

0.00

0.956

Estate

6, 199

6.96

0.001

Age

5, 199

37.43

0.001

T. hunt × Age

5, 199

2.33

0.044

No. of antler points

Intersect

1, 22,19

846.73

0.001

Type of hunt

1, 212

10.03

0.002

Year

1, 212

0.35

0.555

Estate

7, 212

3.33

0.002

Age

5, 212

17.35

0.001

T. hunt × Age

5, 212

0.35

0.877

Factors were type of hunt (commercial or selective) and year, estates were introduced as a random factor, age was introduced as an ordinal factor, and the interaction between type of hunt and age was included in models to see the effect of the type of hunt on every age class and to obtain parameter estimates of Table 3

Table 3

Parameter estimates for the effect of the type of hunt on the dependent morphological variables at each age class resulting from the GLM analyses of Table 2

 

Age (years)

2

3

4

5

6

Body length

Estimate

5.35 ± 5.48

−1.76 ± 4.40

4.62 ± 4.65

1.36 ± 6.47

4.52 ± 5.51

t

0.97

−0.40

0.99

0.21

0.82

p

0.330

0.688

0.322

0.833

0.410

Heart girth

Estimate

9.09 ± 3.38

3.72 ± 2.73

5.25 ± 2.95

4.57 ± 4.02

5.83 ± 3.43

t

2.69

1.36

1.77

1.13

1.69

p

0.008

0.174

0.077

0.257

0.091

Antler length

Estimate

5.46 ± 4.66

5.24 ± 3.91

13.44 ± 4.06

19.91 ± 5.50

4.82 ± 4.92

t

1.17

1.34

3.31

3.61

0.98

p

0.243

0.182

0.001

0.001

0.328

Burr circumference

Estimate

0.50 ± 1.19

0.04 ± 0.96

2.37 ± 1.01

1.22 ± 1.35

1.00 ± 1.21

t

0.42

0.04

2.33

0.89

0.82

p

0.670

0.964

0.021

0.370

0.409

No. of antler points

Estimate

−0.26 ± 1.24

−0.91 ± 1.01

−0.008 ± 1.06

−0.55 ± 1.47

−0.31 ± 1.38

t

−0.21

−0.90

−0.01

−0.37

−0.22

p

0.833

0.368

0.994

0.706

0.819

Type of hunt “selective” and age class “7–11 years” were the reference values, so estimates represent deviations with respect to the effect of “commercial hunt relative to selective hunt at age 7–11”. Table shows mean estimates and their standard errors, t test, and alpha probability

Discussion

Our results show that selective montería differs from commercial montería in the relative size of animals culled, thus selective montería appears to, in general, achieve the goal intended by managers of removing smaller stags. Despite the evident difficulties to make a decision on whether to shoot or not a deer during the brief time when it crosses before the hunter’s position, usually running, hunters culled a sample of animals with smaller body and antlers relative to age than those hunted in commercial hunts. It is also remarkable that although the criteria commonly used in this type of selective hunts is assumed to be based on antler size, body size relative to age also resulted smaller in selective montería, perhaps partly due to its correlation with antler size (Alarcos 2007). Also, for red deer in Spain, Martínez et al. (2005) reported that males hunted in monterías were heavier for their age than those culled in selective hunt, although in this case, selective culling was not performed by selective montería but by selective stalking, and they did not provide data on antler size.

Selective montería affected some ages more than others. On one hand, few mature males were culled in selective montería compared with commercial montería, so most selective effect was focused to ages before maturity. This result tends to conform with recommendations from game management that poor-trophy stags should be removed from the population as soon as possible (e.g., Mesía-Figueroa et al. 1978; Nahlik 1992), although under this criterion, even 19% of males above 4 years of age might be considered too much. On the other hand, the effect of actually selecting smaller individuals was variable among ages for some of the morphological variables. These variations probably reflect the ability of hunters to assess different features. For body size, it seems that young (2-year-old), thin individuals (low heart girth) were clearly differentiated. For antler size, however, the effect was clearer for ages close to maturity (4–5 years) than for younger animals. This results suggest that hunters may be to some extent apply a rule of thumb to shoot deer with antlers below certain size threshold (ca. 60 cm antler length), which would include many young deer and only some really poorly developed older stags.

Our findings support previous considerations that the type of hunt must be taken into account when data are to be used for biological studies (Collier and Krementz 2007), as data obtained from selective monterías are likely biased toward smaller sizes of both body and antlers, and hence, they do not accurately represent the average population. Moreover, since the differences between selective and commercial montería may be larger at certain ages, these data may not represent the actual relationship between development and age of the individuals in the population for transversal studies.

Selectively culling some males by means of selective montería may also have implications for the conservation of Iberian red deer populations. Mortality due to hunting is one of the main artificial interventions in deer populations, producing biased sex ratios (Bubenik 1987; Clutton-Brock and Lonergan 1994; Laurian et al. 2000) and increasing the risk of lost of genetic variability by decreasing effective population size (Ryman et al. 1981; Nunney 1993), reducing the opportunity for sexual selection (Anderson 1994), and altering the selection-drift balance (Hartl and Clark 1997). The structure of populations, as well as the ecological and evolutionary dynamics of ungulate species in Europe, are greatly influenced by human activities such as habitat modification and competition with livestock, among which hunting is especially relevant, because it can act directly not only by artificially increasing natural mortality but also by introducing differential selection over particular types of individuals within populations (Ginsberg and Milner-Gulland 1994; Langvatn and Loison 1999; Milner-Gulland et al. 2003). It has been shown that trophy hunting on individuals shortly before their reproductive peak can have evolutionary consequences in reducing the size of trophies over an ecological time scale (Coltman et al. 2003). In our case, selective montería is acting especially on ages just before reproductive age, which for red deer in Spain peaks between 7 and 9 years of age (Carranza et al. 2004), but the situation may be the opposite to trophy hunting, since selective montería acts against smaller trophies. Moreover, because sexual selection favors larger antlers (Kruuk et al. 2002; Malo et al. 2005), culling individuals with small antlers may represent an additional but not opposite pressure (Ginsberg and Milner-Gulland 1994). However, like many other human interventions, this is of course a source of artificial selection with potential undesirable effects for the maintenance of natural processes (Palumbi 2001; Carranza and Martínez 2002; Coltman 2008). Culling young deer with smaller body and antler size may introduce directional selection toward larger size, but it may also reduce the variability on which natural (and sexual) selection can operate. The evolutionary effect of this form of artificial selection will depend on the heritability of the selected phenotypic traits. Antler size may show little heritability in natural populations of red deer (Kruuk et al. 2002). However, the potential effects of hunting and of selective montería in particular as forms of artificial selection, when they are intense and constant along generations in managed populations of Iberian red deer, deserve further research.

As a form of hunt, selective montería contributes to annual quotas extracted from hunting populations and must be considered as such by managers and administration, but also, moving quotas from commercial to selective hunt also means a displacement of selective pressure from larger to smaller individuals, which may be worth taking into account by conservation authorities.

Acknowledgments

This study was conducted through a collaborative agreement between the University of Extremadura and the government of Andalucia region (Consejería de Medio Ambiente). We thank R. Arenas and the staff at Consejería de Medio Ambiente in Córdoba, as well as L. Arias de Reyna of the University of Córdoba, for their support at different stages of the study. We are also grateful to the owners and wardens of the estates studied. P. Montero, J.M. Seoane, M.J. Taboada, I. Parrillo, M. Núñez, M.J. Brito, and O. Linares helped in fieldwork. C. Mateos helped with statistical analyses. This work complies with current Spanish laws.

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© Springer-Verlag 2008